How to sew on buttons?

Once you have knitted some button holes, how does you sew on the matching buttons? I haven’t seen this talked about in my knitting books. Can you guys give me some tips? Do you use a thinner yarn? Do you tie knots? Thanks for your help.

I’ve separated the yarn I made the sweater with into the individual plies (strands) and used that to sew on buttons.

A few existing threads on this topic:
do you sew buttons on with the yarn you used or…
sewing on buttons
sewing on buttons

Perhaps some insights.

cam